Frequently, it is desirable that a conduit, a pipe or a container which has an open end portion made of resin, have that opening capped with a screw-including retainer fitting. This assures a strong connection with another conduit or pipe, as well as a strong connection permitting the fastening of a cap.
A conventional retainer fitting attached onto an open end portion of a resin pipe is shown in FIG. 11. In FIG. 11, reference numeral 101 generally designates an open end portion of a resin pipe. The open end portion 101 includes a ring-like seal 103 fixed onto its outer circumferential surface near an open end 102 and a crimping groove 104 that extends circumferentially about the outer circumferential surface of portion 101 and positioned farther away from end 102 than seal 103.
The retainer fitting, generally indicated at 105, assumes the form of a double pipe structure including an inner cylinder portion 106 covering an inner circumferential surface of the open end portion 101. The inner portion 106 includes a screw-like thread 106a projecting centripetally. Retainer 105 also includes an outer cylinder portion 107 formed integrally with the inner cylinder portion 106 and covering an outer circumferential surface of the open end portion 101 and extending about the open end 102.
After the open end portion 101 is capped with the retainer fitting 105, the seal 103 is pressed centripetally by the outer cylinder portion 107 of the retainer fitting 105 to thereby achieve a hermetic at the location of seal 103. At the same time, a sectionally L-shaped crimping rib 107a is formed in the outer cylinder portion 107 and received in the crimping groove 104 to thereby integrally attach the retainer fitting 105 onto the opening end portion 101.
In the conventional retainer fitting 105, there is however a risk that the inwardly directed force of the outer cylinder portion 107 centripetally pressing against seal 103 may be weakened due to distortion generated in the retainer fitting 105 when the crimping rib 107a is formed. This is because the crimping rib 107a is formed after the open end portion 101 is capped with the retainer fitting 105 in a condition in which the inner cylinder portion 106 and the outer cylinder portion 107 act on each other so that the distance therebetween is reduced.
There is also a risk that the fastening force may be weakened by relaxation of stress of the resin forming the open end portion 101, or the like, especially during long-term use that can result in the rotation of the retainer fitting 105 relative to end portion 101.
Another example concerns an opening in the form of a fuel inlet for a fuel tank, or the like, as shown in FIG. 12. The retainer fitting 202 again includes a screw-like thread 202a and is attached to the inside of an iron pipe 201 by welding. A resin ring 203 is provided on the outer circumference of the iron pipe 201 for the purpose of sealing between the iron pipe 201 and a body-side inlet box (having a duct in which the fuel inlet portion projects).
Such a configuration is not only complex in structure, because the number of parts is no less than three, but involves a large cost because of the aforementioned welding work.
FIG. 13 shows an improved a resin pipe constituted by only two parts where a double tube type retainer fitting is attached to the open end of the resin pipe. In the resin pipe provided with this double tube type retainer fitting, a ring-like seal 205 is fixed on an outer circumferential surface near an open end 204a of the end portion 204, and a Crimping groove 206 is formed circumferentially on an outer circumferential surface further from the open end 204a beyond seal 205.
The retainer fitting 207 assumes the form of a double tube structure comprising an inner cylinder portion 208, covering an inner circumferential surface of the end portion 204 and having a screw-like thread 208a projecting centripetally, and an outer cylinder portion 209 formed integrally with the inner cylinder portion 208 and covering an outer circumferential surface of the end portion 204a round the open end 204a.
After the retainer fitting 207 is attached onto the end portion 204, the seal 205 is pressed centripetally by the outer cylinder portion 209 to thereby achieve a hermetic seal at seal 205. At the same time, a sectionally L-shaped crimping portion 209a is formed by crimping in the outer cylinder portion 209 so that the crimping portion 209a will fit into a crimping groove 206 to thereby integrally attach the retainer fitting 207 onto the end portion 204.
The end portion 204 is formed so that the outer diameter and thickness thereof are both large for the purpose of sealing between the end portion 204 and the body-side inlet box.
It should be understood that the diameter of the duct of the inlet box, the diameter of a cap fitted to the inner cylinder portion and the general size (outer diameter) of the resin pipe are each determined preliminarily because the need for use with existing parts. That is, the gap (through the resin pipe) between the duct of the inlet box and the cap is set to be a fixed size because of existing parts.
Further, because the resin pipe is formed by blow molding, there is a limitation that the thickness of the resin pipe cannot be changed greatly as shown in FIG. 13 and it is virtually impossible that only the end portion can be made thick.
Accordingly, in the case where the double tube type retainer fitting is put on the resin pipe which is formed by blow molding so as to be entirely thin like a filler, it is necessary to fill up the gap between the resin pipe and the inlet box, that is to reduce the gap to thereby bring the gap close to a value in which a sealing material is fitted properly, to thereby secure the sealing characteristics of the fitting.
It is now thought of that the retainer fitting is made to carry out the function of filling up the gap between the resin pipe and the inlet box. In the configuration of this case, after the inner cylinder portion of the retainer fitting is fitted to the inside of the linear resin pipe and a gap is formed between the outer cylinder portion of the retainer fitting and the outer circumferential surface of the resin pipe, the distance between the inlet box and the outer cylinder portion of the retainer fitting is reduced to thereby perform sealing securely.
In the case where the inner cylinder portion of the retainer fitting is fitted to the resin pipe, the state of attachment of the retainer fitting is, however, unstable.
On the other hand, in order to make the resin pipe per se carry out the function of filling up the gap between the resin pipe and the inlet box without an increase of the thickness thereof, it may be thought of that molding is made so that the diameter of the end portion of the resin pipe is enlarged.
In this case, however, there arises a problem that the cap fitted to the inner cylinder portion is unstable.